The present invention relates to an electronic device for the infusion of ionic drugs in medical iontophoresis. In particular, the present invention relates to a multiple site iontophoresis electronic device which is capable of driving a plurality of electrodes with a single controller.
There is an ongoing search for methods of medical treatment which are noninvasive and painless. An effective treatment is useless if the patient refuses it due to the pain it can cause. Iontophoresis medication delivery systems are safe, effective, noninvasive and relatively painless.
Iontophoresis involves the interaction between ionized molecules of a drug and an external electric field, resulting in the migration of charged molecules. The migration is achieved by placing two electrodes on the patient's skin which are connected to an electric DC power supply. One of the electrodes is a source or "active" electrode filled with a drug solution. The other electrode is a return or "inactive" electrode filled with an electrolyte solution. The electric field generated between the two electrodes causes the charged drug molecules to migrate from the active electrode into the tissues and blood stream of the patient without the necessity of hypodermic injection and its adverse effects, such as pain and risk of infection. Iontophoresis tends to diffuse the drug throughout the treated tissue whereas an injection amasses a concentrated bolus of drug within the tissue or joint, potentially causing damage to the tissue.
There are two major disadvantages of iontophoresis. The first is skin irritation from acid-base concentrations created by electrolysis of the solution. The second is the slowness of drug delivery through the electrode.
Skin irritation can be reduced by chemically buffering within the electrode the H+ions produced by electrolysis. This method is disclosed in Johnson U.S. Pat. No. 4,973,303, for example. Skin irritation can also be decreased by reducing the current intensity through the electrode, or by activating the electrode for short periods, followed by rest periods.
One attempt to reduce dosage delivery time includes the use of a bifurcated lead wire connected between a single channel electrode driver circuit and two pair of electrodes with a common return. The bifurcated lead wire poses a problem. A human, transcutaneous load can vary from one hundred ohm to twelve thousand ohms, depending upon the location of the electrodes on the patient's skin. Since the driving current is constant, it will divide according to each electrode resistance, resulting in unequal diffusion from each electrode. Even if the electrode impedance could be balanced, the single output drive must provide a current intensity of two times the current intensity required for a single electrode pair to achieve comparable results. Further, the bifurcated lead wire can only drive electrodes containing drug solutions with the same polarity. This prevents simultaneous delivery of positive and negative polarized drug solutions.